The invention relates generally to copying.
More particularly, the invention relates to a method and apparatus for the reproduction of a colored original.
A known apparatus for the reproduction of a colored original has a measuring unit for determining the proportions of the primary colors red, green and blue in the original. The measuring unit includes three sets of photoelectric cells, and each set is sensitized to one of the primary colors. A respective color filter is disposed in the optical path leading to each set of cells and the transmissivity of each color filter corresponds approximately to the spectral sensitivity of the copy material in the same color. The copying apparatus further comprises a lamp housing containing a source of copy light in each primary color, and a mixing device for the copy light of different color.
The West German Offenlegungsschrift No. 33 17 804 discloses an apparatus which is designed to produce color copies and has separate measuring and copying stations. The spectral sensitivity of the measuring unit is equated to the spectral sensitivity of the copy material with a high degree of precision by appropriate selection of the transmissivities of the measuring unit filters.
There are problems in adjusting the measuring unit filters to the spectral sensitivity of the copy material. On the one hand, it is generally difficult to produce color filters having a predetermined spectral transmissivity curve or function. On the other hand, the spectral sensitivity curves or functions of the various color copy materials on the market can differ so greatly that the filters for the measuring unit must be manufactured to meet the specifications cannot be universally employed but must be manufactured to meet the specifications of a particular type of copy material only. Moreover, the transmissivities of a set of measuring unit filters can change due to external influences such as temperature, dust deposits, etc.
The West German Patent No. 1 214 525 discloses an apparatus for additive color copying. The apparatus includes three sources of copy light each of which is associated with a copying filter designed to pass light in one of the primary colors. The three beams of radiation are simultaneously passed through an original to be copied via a reflector arrangement and the exposures in the three primary colors are begun at the same time. A portion of the radiation which has travelled through the original is deflected towards beam splitters having color filters disposed downstream thereof. After splitting, this portion of the radiation enters a measuring unit which determines the intensity in each of the three primary colors. The radiation emitted by each of the three light sources is then regulated over time in dependence upon the amount of light required for the copying operation.
This known additive copying procedure has the drawback that it is not possible to calculate the required amounts of copy light in advance. Thus, measurement and evaluation of the portion of the radiation used for intensity determination are performed at the time of copying.